1. Technical Field
The present invention relates to an apparatus for changing the speed of bicycles and other vehicles using sprockets and chains. More particularly, the invention is a transmission apparatus for changing the speed of such vehicles using inner gears within a rear wheel hub and controlling the inner gears with controllers mounted on a hub shaft, so that the bicycle or other vehicle has a good appearance, changing speed is convenient, the effect occurs immediately after a speed-changing operation, little noise occurs when changing speed, and the number of speed level steps may easily be increased.
2. Background Art
In general, the apparatus for changing speed (i.e., the transmission) is installed on a bicycle. However, in some cases, the transmission may be installed on wheelchairs and toy cars using pedals.
In a conventional bicycle transmission, sprockets having differing diameters, are mounted, respectively, on the side of the middle frame and rear wheel, and a chain connects the front and rear sprockets. The speed is changed by changing the coupling of the sprockets.
But the conventional bicycle transmission has a few drawbacks in that it is too bulky because of the many large sprockets, and noise and impacts occur when changing speed.
As a means of overcoming these drawbacks, an inner gear-type transmission may be installed in the rear wheel hub. In such an inner gear-type transmission, small gears and a controlling means are disposed in a hub shell, so that the bicycle speed is changed by changing the gear tooth ratio thereof.
Illustrative of an inner gear-type transmission is Japanese laid open patent publication No. Hei7-10069, which discloses an inner-gear type transmission hub for bicycles.
The prior art inner gear-type transmission, as shown in FIG. 1, comprises a speed changing portion 10, composed of a hub shaft 6, a driving body 2, a freely rotatable hub 1, at least two sun gears 12, 13 engaging at least two tooth portions 11a, 11b, and a speed-change controlling portion 20. The latter controls the speed-changing portion 10 by transforming the rotational state of the sun gears. The speed-changing portion is composed of a one-directional driving means 7 that is installed between the driving body 2 and the hub 1, enabling the hub 1 to rotate over the driving body 2. A ring-gear portion 1c is fixed to the hub 1 engaging planetary gears 11.
The transmission can change the bicycle speed into three states: a low speed state, in which the driving force of the driving body 2 is transferred to the hub 1 via the one-directional driving means 7 by controlling of the speed-change controlling portion 20; and at least two high speed-states, in which the driving force of the driving body 2 is transferred to the ring-gear portion 1c via the planetary gears 11, resulting in a speed increase.
In other words, when it is in the low speed state, the driving force of the driving body 2 is transferred directly to the hub 1 by the one-directional driving means 7. However, when the rider controls the speed-change controlling portion 20, one of the sun gears 12, 13 is fixed selectively. The driving body 2 is rotating, in this state, the ring-gear portion 1c rotating by planetary gears 11 engaging the selectively fixed sun gear.
In this case, the speed is controlled by the tooth ratio among the fixed sun gear, the planetary gears 11 and ring-gear portion 1c. Because the fixed sun gear has many more teeth than the planetary gears 11, the speed of the planetary gears 11 revolving around the fixed sun gear exceeds the speed of one-directional driving means 7, thus yielding the high speed state.
As shown in FIGS. 2A to 2C, the prior art speed-change controlling portion 20 is operated by pawls 12a, 13a mounted on the side of the sun gears 12, 13, with a protrusion for fixing gears 6a, and a controlling sleeve 21. Each step of changing speed is operated by using the pawls 12a, 13a to fix the sun gears to the controlling sleeve 21 or to release the sun gears from the pawls 12a, 13a. 
In the low speed state, as shown in FIG. 2A, the two pawls 12a, 13a are released from the controlling sleeve 21 by the protrusions of the fixing gears 6a. But in the first high speed state, as shown in FIG. 2B, because one pawl 12a is fastened to the controlling sleeve 21, one sun gear 13 is rotatable. So the larger diameter portion of the planetary gears 11 engages the fixed sun gear 12.
On the other hand, when the other pawl 13a is fastened to the controlling sleeve 21, the other sun gear 12 is rotatable, so that the smaller diameter portion of the planetary gears 11 engages the fixed sun gear 13, as shown in FIG. 2C. This is the second high speed state.
However, in a speed control apparatus as described above, because the two pawls 12a, 13a are installed opposite one another, there is a drawback: When a rider operates a lever in order to change the speed of the bicycle, the effect of this operation is delayed until one of the pawls 12a, 13a is activated. Typically, the effect of the operation occurs only after the wheel makes a half revolution.
While the above drawback could be resolved somewhat by providing more pawls, this would necessitate changing the shape of the controlling sleeve 21. But because it would also be necessary to change the shape of the protrusions of the fixing gears 6a, the number of pawls could not easily be increased.
Even when the pawls are not in operation, friction always occurs between the pawls 12a, 13a and the controlling sleeve 21. This friction causes noise and abrasion, which is also a negative factor.
Moreover, if more speed change steps are offered by providing more planetary gears, the above drawbacks become more serious.
It is an object of the present invention to provide an apparatus for changing the speed of bicycles, which changes speed by using inner gears inside a rear wheel hub and controlling the inner gears with controllers mounted on a hub shaft. Accordingly, the bicycle has a good appearance, changing speed is convenient, the effect of the speed change operation occurs immediately, little noise occurs during the operation, and additional speed level steps may easily be provided.
According to the above object, there is provided an apparatus for changing the speed of bicycles, comprising: a driven sprocket receiving the driving force of a driving sprocket; a speed controlling portion, comprising a carrier fixed to one side of the driven sprocket, containing a plurality of planetary gears having ratchet-teeth formed along their inner circumferences; at least two sun gears engaging each step of the planetary gears; a ring gear engaging the other sides of the planetary gears; an output portion, comprising a hub shell transferring the driving force to the rear wheel by means of the carrier and the ring gear; a clutch means, mounted between the carrier and hub shell, and the ring gear and the hub shell, which selectively mediates the driving force; and a speed-change controlling portion.
The latter comprises a hub shaft having a pawl-positioning portion; at least two sets of pawls engaging with or releasing from the ratchet-teeth of the two or more sun gears; a pawl-controlling ring controlling the position of the two or more sets of pawls; a transforming disk having a groove along its outer circumference with a hooking portion formed at a certain position thereon, in order to transform the position of the pawl-controlling ring via a mediating portion; a spring for restoring the position of the transforming disk to its original position; and a spacing portion enabling the transforming disk to rotate freely.